Net::FTP will allow you to deal with FTP sessions.

You can't FTP to a machine that isn't running an FTP server.
I'm not sure if it's possible to check for the status returned when FTP commands fail - I'm pretty sure it is possible, but I'd have to RTFM.

Your question is rather unclear - are you trying to connect to a remote box and carry out an FTP transaction, or are you trying to monitor a system locally by FTP'ing to yourself and/or run a command like 'top' or 'ps'?

Update: Thinking about this, some well placed error checking (eval statements? Don't quote me on that) should let you know if the initial connection attempt to the FTP server failled...